1. (Field of the Invention)
The present invention generally relates to the facilitation of fabrication of cathode ray tubes or similar products and, more particularly, to a method of forming on cathode ray tubes respective identifying indicium which provide readable information used to control the production and/or stock administration of the cathode ray tubes.
2. (Description of the Prior Art)
In most automated production lines, the use is made of an automatic production identifying system for automatically identifying the type, model, lot number, serial number and/or any other characteristics of products being assembled or inspected. To facilitate this automatic product identification, one method now widely practiced is that products are applied with adhesive tags each bearing an identifying indicia so printed thereon as to be read by an automatic code reader. The indicia includes, for example, a unique bar code or any other marking and represents readable information peculiar to the particular product being made, for example, the type, model, lot number, serial number and/or characteristic of the particular product being made.
When it comes to the manufacture of fabrication of cathode ray tubes, the production line includes several heat treating stations and several chemical treating stations through which cathode ray tubes being manufactured are transferred in specific sequence. The presence of the heat and chemical treating stations in the production line makes it difficult to use the adhesive tags of the above described type on the cathode ray tubes.
However, any one of the Japanese Laid-open Patent Publications No. 55-155450, published in 1980, and No. 60-81744 published in 1985 discloses a method of forming that identifying indicia on a glass envelope or enclosure of each cathode ray tube which exhibits excellent resistance to both heat and chemicals. Specifically, according to the first-mentioned publication, the identifying indicia is in the form of a bar code formed by the use of a carving technique, that is, in the form of a bar code carved on a particular portion of the glass envelope of the cathode ray tube. On the other hand, according to the second-mentioned publication, the identifying indicia is in the form of a bar code formed by the use of a heat resistant marking agent such as a colored frit, which code is imprinted on a particular side portion of the glass envelope of the cathode ray tube. In both of these publications, the identifying indicia is adapted to be read by an optical or magnetic code identifier.
Apart from the disclosure made in any one of the above mentioned publications, attempts have been made to form, on a portion of the glass envelope of the cathode ray tube, a predetermined pattern of traces of fusion by the use of a high density energy radiator such as a laser, so that an optical code identifier can read such pattern of traces of fusion.
It has, however, been found that all of the above discussed prior art methods have their own problems. More specifically, where the heat resistant marking agent such as the colored frit is employed to form the identifying code on each cathode ray tube, the actual formation of the identifying code on the cathode ray tube relies only on the employment of a printing technique or a stencil printing technique and, therefore, much difficulty has been encountered in controlling the amount of the marking agent to be applied. In addition, even though the identifying code has successfully been formed on the cathode ray tube, particularly an intended portion of the glass envelope, the identifying code so formed tends to distort and/or break off, thereby posing a problem in that a high quality and reliable identifying code can not be formed uniformly on all of the cathode ray tubes being manufactured. This problem in turn makes it difficult for the automatic code identifier to read the identifying code properly.
On the other hand, where the identifying code is in the form of either the patterned carvings formed by the use of a cutter, or the patterned traces of fusion formed by the use of a high density energy radiator such as a laser, the identifying code which can eventually give a high ratio of contrast, that is, a high difference in reflectance between radiated and non-radiated portions of the identifying code, can not be formed unless each carving or trace of fusion so formed has a required depth and width. This requirement makes it difficult to form the identifying code that is minute and of a complicated shape.